Apparatus for the drying of sheet material

ABSTRACT

An apparatus for applying heated air to the surface of a sheet material has a dryer surface at an outer wall of a boxlike structure, the dryer surface being defined by alternate openings and apertured surface regions in the said outer wall, the apertured surface regions being connected together inwardly of the boxlike structure and being isolated from the openings, and a substantially closed air circulation system is developed by the apparatus when in use, air passing outwardly through the apertured surface regions and inwardly through the openings, or vice versa, during the surface treatment of a sheet material arranged in closely spaced adjacent disposition relative to the dryer surface. For simultaneous treatment of both surfaces of a sheet material two apparatuses as aforesaid will be used, such apparatuses being arranged in opposed closely spaced disposition with the material passing therebetween, and the air circulation systems of the individual apparatuses will be isolated one from the other to enable independent treatment conditions to exist at the opposite sides of the material.

United States Patent [72] Inventors Raymond Victor Evans Blackburn,England; John Edward Hibbitt, Darwen, England [21] Appl. No. 807,855[22] Filed Mar. 17, 1969 [45] Patented May 4, 1971 [73] AssigneeSinger-Cobble Limited Blackburn, Lancashire, England [32] Priority Mar.18, 1968 [3 3] Great Britain [3 1 12970/68 [54] APPARATUS FOR THE DRYING0F SHEET MATERIAL 14 Claims, 7 Drawing Figs.

[52] U.S. Cl 34/155 [51] Int. Cl F26b 13/02 [50] Field of Search 34/155,162, 164

[56] References Cited UNITED STATES PATENTS 1,642,928 9/1927 Kocha34/162 3,151,950 10/1964 Newman et al. 34/155X 3,371,427 3/1968 ThygesonABSTRACT: An apparatus for applying heated air to the surface of a sheetmaterial has a dryer surface at an outer wall of a boxlike structure,the dryer surface being defined by alternate openings'and aperturedsurface regions in the said outer wall, the apertured surface regionsbeing connected together inwardly of the boxlike structure and beingisolated from the openings, and a substantially closed air circulationsystem is developed by the apparatus when in use, air passing outwardlythrough the apertured surface regions and inwardly through the openings,or vice versa, during the surface treatment of a sheet material arrangedin closely spaced adjacent disposition relative to the dryer surface.

For simultaneous treatment of both surfaces of a sheet material twoapparatuses as aforesaid will be used, such apparatuses being arrangedin opposed closely spaced disposition with the material passingtherebetween, and the air circulation systems of the individualapparatuses will be isolated one from the other to enable independenttreatment conditions to exist at the opposite sides of the material.

PATENTEUHAY 4m 3.577552 SHEET H []F 4 INVENTORS 54/0100! I/Ic ran Ewan 1APPARATUS FOR THE DRYING or SHEET MATERIAL Theinventionconcernsiapparatus for't he heating, drying,

' and/or curing, or other treatment of sheet materials or of coatingsapplied thereto, hereafter, for convenience, referred to simply asapparatus for drying sheet material, and has par- I tufted carpetproblemsare met with in view of the comparatively large quantity ofliquids which, of necessity, must be removed in a short period of timeif the overall drying time is to be held within practical limits.

It is known to dry a weblike material by applying heated air connectingsaid openings, the apertured surface regions and.

openings being isolated one from the other inwardly of the said surface,and air circulation means adapted to feed air to the apertured regionsthrough the first said ducting and to receive air from theopeningsthrough the second said ducting, the whole being adapted to define,together with a web located adjacent the dryer surface, an independentclosed air recirculation system for the treatment of a web at a surfacethereof.

A heat exchange means will usually be provided in the path of the air,such means being adapted to apply heat to or to 7 remove heat from suchair during the circulation thereof.

to a surface-of the material at one location and to apply a reduced airpressure at an immediately adjacent location so as to give rise to anair circulation at the surface fordrying purposes. Apparatus forpracticing this method comprises a closed body part through which thematerial under treatment passes, areas of perforations and aperturesarranged alternately in the intended direction of movement of thematerial, a fan at each lateral edge of the said material and arrangedto supply air to the areas of perforations and to draw air inwardlythrough the apertures, and a heater rneans through'which the air passesin its path of movement from the apertures to the fan. In the aforesaidapparatus the arrangement is such that both surfaces of the material aresimultaneously subjected to a drying treatment, the rotational axes ofthe fans lying in the plane of the web and each such fan supplying airboth to the top and to the bottom surface of the weblike material.

In the apparatus aforesaid, both top and bottom surfaces of the materialare subjected to a like treatment, the apparatus being of such characteras to preclude the possibility of treating a single surface only and ofisolating the other surface during such treatment.

Furthermore,' the provision of a fan adjacent each lateral edge of thematerial under treatment gives rise to an unfavorable air circulationpattern in that, generally, each fan creates an airflow pattern at oneside only of the apparatus, each such airflow pattern reaching above andbelowthe material at one side thereof. It is possible that in practicethe'weblike material will be subjected to a nonuniform treatmentthroughout its width at each surface. The utilization of a separateheater means at each face of the material and for each fan will increasethe possibility of a nonuniform treatment since tem In a preferredembodiment the second said ducting is defined in part by thedryercasing, the alternately disposed apertured regions and aperturesdefining a wall of such casing, and the first ducting is disposedinwardly of the casing.

Preferably the apertured surface regions and openings are arranged insuccessive side-by-side dispositions in the trans verse direction of thedryer, the axes of the apertured regions and openings being inclined tosuch transverse direction so as to give an overlap of successiveapertured regionis when viewed in the direction of movement of thefabric being dried. In practice it will be usual to provide a pluralityof dryers as aforesaid, each such dryer being paired with another likedryer and being arranged in closely spaced opposed disposition relativethereto to allow passage of the material therebetween. Preferably, theseparation of the dryer surfaces The primary object of the presentinvention is to provide an apparatus for drying sheet material whichavoids the aforementioned difficulties and allows of the uniformtreatment of the whole of one surface of a weblike material to theexclusion of the other surface thereof.

According to the present invention apparatus for drying sheet materialcomprises a closed boxlike structure having an outer surface thereof,which surface constitutes the dryer surface, defined by openings andapertured regions, and an air circulation means withinthe structure andadapted to apply pressure air to the apertured regions for dischargefrom the box through such regions and to apply a reduced pressure in theregion of the openings to draw air inwardly through such openings, theopenings and apertured regions being so adapted and arranged as to givea substantially even distribution of airflow outwardly of the surface.

I Preferably, the apparatus includes a plurality of apertured surfaceregions and openings which collectively define a dryer surface, suchregions and openings being arranged alternately and in immediatelyadjacent disposition so that all sections of a surface of a materialunder treatment and moving relative to the dryer surface in thelongitudinal or transverse direction of the apparatus are subjected toalike treatment, a first ducting connecting said apertured surfaceregions, a second ducting of the opposed dryers does not exceed 4inches.

The invention also includes the combination of an apparatus as aforesaidwith one or more like such apparatuses.

The invention will now be described further by way of example only withreference to the accompanying drawings illustrating one embodimentthereof and in which:

FIG. I is a perspective view, from below, of a dryer module constructedin accordance with the present invention;

FIG. 2 is a transverse section through the module of FIG. 1;

FIG. 3 is a section taken on line III-III of FIG. 1;

FIG. 4 is a vertical section, drawn to an enlarged scale, through anexplosion panel as fitted to the module and taken on line IV-IV of FIG.5;

FIG. 5 is a perspective view from one end of a dryer embodying four ofthe modules as shown in FIG. 1;

FIG. 6 is a diagrammatic perspective view of a baffle arrangement asembodied in the dryer shown in FIG. 5 for the purpose of reducing heatlosses between the dryer and the atmosphere and between upper and lowersections of the dryer; and

FIG. 7 is a diagrammatic representation of the air exchange which takesplace within the dryer during usage thereof, the dryer being viewed fromabove.

Referring now to the drawings, and-particularly to FIGS. 1 to 3 thereof,a dryer module comprises a heat'insulating casing ll, a plurality ofapertured surface regions 12 and openings 13 arranged alternately at oneface of the casing and defining a wall thereof, an air circulation means14 extending within the casing, such means receiving air from outsidethe casing through the openings'13 and delivering air to the aperturedsurface regions 12 for discharge therethrough, a first ducting l5connecting the apertured regions and putting same in communication withthe air circulation means 14 at the output side thereof, and a secondducting 16connecting the openings and putting same in communication withthe inlet side of the air circulation means.

The casing 11 is generally rectangular, having spaced sidewalls Ila andend walls llb, and a top wall 11c. The un- 3 The first" ducting l5, seeFIG. 3, basically comprises a passageway defined by spaced sidewalls 15aand a top cover 15b, the said sidewalls being outwardly cranked at thelower regions thereof, as at 15a, to extend to the lower edge of thecorresponding wall Ila of the casing and the top cover having a firstpart which is disposed substantially horizontally and a second partwhich extends downwardly away from the said first part. The ducting iscompleted by forward and rearward end walls 15c respectively, such wallseach having upper and lower regions 15c joined by an horizontal plate15:" and each extending downwardly to the underside of the casing.

The ducting is also provided with a transverse body 15d which acts inthe nature of a partition to define on either side thereof and at therespective ends of the ducting forward and rearward outlet. ports 15e,15f to the said ducting and an inclined baffle 15g is positioned withinthe ducting to divide the airflow from the fan which constitutes the aircirculation means 14 between such forward and rearward ports, the saidbaffle 15g being disposed forwardly of the transverse body in thedirection of airflow.

The apertured surface regions 12 aforesaid are constituted by aperturedplates which extend across the outer end of the ducting l5 and in theplane of the underside of the casing 11, the said plates being arrangedin spaced parallel disposition and each being inclined to a lineextending between and at right angles to the sidewalls 11a of suchcasing. The dimensions and the angle of inclination of the plates issuch that successive such plates overlap in the direction of motion of aweb thereby. By providing the diagonal arrangement of the plates it ispossible to pass a material under processing in either of two directionswhich are mutually inclined at 90 one such direction corresponding tothe widthwise direction of the module and the other the lengthwisedirection thereof.

An iris-type baffle or some alternative damper means, not shown, may beprovided to allow of the control of air velocity from the fan, ifdesired.

The second ducting 16 is defined in part by the upper regions of thecasing outwardly of the first ducting and in part by transversepassageways 16a extending along the lower edge of the casing andinwardly thereof, the said passageways being in communication with thesaid upper region and also with the openings 13 in the underside of thecasing. The transverse passageways 16a are each constituted by therespective sidewalls Ila of the casing, the sidewall 15a of the firstducting arranged in spaced disposition relative thereto, the downwardlyand outwardly inclined extremity 15a to such wall, and an horizontalplate 16!; extending between the said sidewalls and at a positionapproximately at or slightly below the lower edge of the explosionpanels 17. The passageways are joined together by conduits 16c extendingtherebetween and disposed at the lower edges and inwardly of the casing,

such conduits having sidewalls defined by the end walls of the casingand the end walls of the first ducting and lower and upperwallsconstituted by a wall of the casing and an additional top plate 16crespectively. An opening 16d is provided in the top of one of theconduits whereby such conduit is put in communication with the upperregion of the casing.

The second ducting is completed by means Me which isolate the openings13 from the apertured regions, such means comprising two spaced sideplates Me for each openings, which plates are of inverted W-shape andextend inwardly of the casing from the adjacent edges of two successiveapertured plates, and two mutually inclined cover plates l6e" arrangedwithin the angle of the side plates, the outer edges of the side platesengaging the underside of the cranked lower regions 15a of the sidewallsof the first ducting. Each opening 13 is put in communication with thetransverse passageways 16a by through apertures 18 in the cranked lowerregions aforesaid. Preferably, the successive openings 13 are ofreducing size towards the heater end of the module thus to facilitatethe maintaining of a unifonn treatment at all regions widthwise of thematerial under processing.

An explosion panell7 is shown in cross section in FIG. 4 and comprises abody 17a of heat insulating material supported between two spaced,frangible plates 17b, the. said body and plates being mounted relativeto an opening Ila in the respective sidewall 11 by a rectangularclamping strip 17c secured to the outer wall of the casing. The innerface of the panel presents a rigid mesh structure 17d thereby to imparta requisite amount of rigidity to the panel as a whole. The innermostplate bears against the outwardly facing surface of a lip formed in thesidewall, whilst the outermost plate bears against the outer surface ofthe wall about the periphery of the opening, the clamping strip 170overlying the edge of the plate and being secured to the casing byscrews l7e arranged outwardly of the periphery of the plate. Preferably,the frangible strips are fabricated from Superite" whilst the heatinsulating material comprises soft glass fiber wadding sold under TradeName Cosywrap.

The air circulation path for the dryer is indicated by the arrows'inFIG. 2 of the drawings and it will be seen that the fan 14 draws airpast the burner 17 to the lower pressure side of the fan and such heatedair is fed to the first ducting 15. The air then passes along the saidducting through the forward and rearward outlet ports to the aperturedplates, the said air issuing from the apertures in such plates as amultiplicity of pressure jets which impinge on a web or like materialmoving adjacent to the said plates. The openings are connected with thelow pressure side of the fan and hencea reduced air pressure is appliedin the region of the openings, thus being drawn from adjacent thesurface of the web and passing through the passageways to the conduitand thence, via a filter member, to the region of the burner and finallyback to the fan for continu'ed circulation.

Any moisturepicked up from the web by the heated air will be drawn intothe casing and by arranging that the air within the casing iscontinually replenished by outside air at a controlled rate and thatmoisture laden air is exhausted to atmosphere, so the drying of the webcan be effected.

In practice it will be usual to utilize a plurality of the dryer modulesof the character of that shown in FIGS. 1 to 3, and a typicalinstallation is shown in FIG. 5 where four modules are employed.

Thus, referring now to FIG. 5, four dryer modules of the character ofthat described with reference to FIGS. 1 to 3 are provided, the modulesbeing arranged in closely adjacent opposed spaced disposition. Eachmodule has its own burner and air circulation means and each of themodules is separately controllable.

The relative dispositions of the individual modules 20 whichcollectively define the dryer shown in FIG. 5 are such as to provide anarrow slot 21 through which a material 22 under processing, say atufted carpet or like material, passes, the material being supported onand progressed by a stenter 23 which extends through the unit from frontto rear. Conveniently the stenter 23 will be adjustable as regards itswidth thus to allow of the processing of materials of different widths.A baffle arrangement 24 will be provided adjacent the laterally movablestenter chain, which movement is effected by any convenient screw orworm drive means 25 in a manner known per se, thus to prevent heatexchange between upper and lower dryer sections, to avoid heat lossesfrom the dryer, and to preclude uncontrolled ingress of outside air.

The baffle arrangement 24 is shown diagrammatically in FIG. 6 and willbe seen to comprise a first vertical baffle 24a extending between thelaterally movable stenter chain and the end of the slot 21, such baffleserving to close the slot 21 in such region, a second vertical baffle24b extending along the line of the adjustable stenter chain anddisposed within the dryer and an horizontal baffle 24c likewise withinthe dryer and separating upper and lower dryer sections in the regionoutwardly of the adjustable stenter.

The first vertical baffle 24a is a ribbon baffle, the strip a casing inwhich the said strip is coiled.

The horizontal baffle 24c is best seen in FIG. 6 and comprises aplurality of flat elongate elements 24d pivotally secured together as byrings 24c and suspended from tracks 24f by runners 24g. As theadjustable stenter moves back and forth so the mutual inclinations ofthe elements are varied to increase or to reduce the effective length ofthe baffle.

Various guide rollers 26, and delivery and takeup rollers 27, 28 areprovided, such rollers being driven or not as required.

Access hatches or doors 29 are provided, in the casing of the dryer, asappropriate, and the casing as a whole is insulated against heat losses.The necessary pipework (not shown) for the combustible fuel will ofcourse be provided, as will appropriate exhaust ducting.

The air circulation within the dryer illustrated in FIG. 5 is showndiagrammatically in FIG. 7. Referring now to FIG. 7 of the drawing, thematerial 71 under processing moves in counterdirection to the movementof the air 72, the air entering initially through an adjustable inletlouvre 73, being circulated within module A, and being transferred, intime, to module B via opening 74 and eventually extracted for dischargeto atmosphere through conduit 75. With this arrangement the driestregions of the carpet are subjected to treatment from newly introducedair, or more properly the air having a proportion of newly introducedair, whilst the more moist but equally warm air is applied to thewettest regions of the carpet.

The upper and lower regions of the dryer are isolated one from the otherby the material under processing and the horizontal baffle, and not onlydo such regions have an independent air circulation but such aircirculations may well have significantly different temperatures. Forexample, in one example the temperature of the upper air circulation maybe of the order of 450 F. whilst that of the lower circulation may beapproximately 200 F.

In another arrangement, not shown, a dryer module is used in combinationwith a fixed support surface, the module being disposed in spaced apartrelationship with the said surface to define a web-receiving spacetherebetween. The surface will have a heat resistant facing thereto orwill be defined by such a material.

We have found that by means of the dryer hereinbefore described we areable to remove the moisture from a latex backed floor cover at a ratewhich bears very favorable comparison with that achieved by conventionaldryers. Furthermore, the utilization of a multitude of jets of pressureair arranged in closely adjacent disposition will assist in thesupporting of the material during its passage through the dryer and willin consequence, enable the material to be held at its full width with noor only minimal sag and will thus facilitate the uniform treatment ofthe material. In the event of fan failure, the stenter will maintain thematerial at its full width without sag.

Whilst in the arrangements hereinbefore described and illustrated theheating of the air has been by means of a gas or like burner, in no wayis the invention so restricted in that alternative means may be found tobe preferable in some circumstances. Thus, for example, a heater coilmay be provided in the path of the airflow instead of utilizing a gas orother burner, the coils being located, for instance, in the positions Cas indicated in FIG. 2 of the drawings. It should be borne in mind thatin some circumstances the requirement may be that heat is withdrawnrather than applied in which case the coils would form a part of arefrigeration or like circuit. In still other circumstances no heatexchange requirement will exist for the circulating air, save for thatbetween such air and the material under treatment, and thus there willbe neither heater nor cooler means within the dryer.

Furthermore, whilst the primary application of the dryer is thought tobe in the context of drying the synthetic latex backing of tufted carpetor like materials, in no sense is theapplication limited to thisspecific field or to this particular purpose, since the dryer may wellbe capable of utilization in connection with any web or sheet materialfor the drying thereof or for any other treatment where controlled aircirculation is necessary.

We claim:

1. Apparatus for drying sheet material comprising a cabinet havingoppositely disposed end walls and sidewalls, air supply duct meanswithin said cabinet for supplying a source of high pressure drying air,a dryer surface including a plurality of spaced apertured high pressureduct means operatively connected with said air supply duct means andhaving their apertures disposed for directing drying air toward thesurface of a moving web, said apertured duct means being disposed at aninclined angle to a line "extending between and at right angles to saidsidewalls of said cabinet such that successive areas of said aperturedduct means overlap said web relative to the direction of travel of saidweb, return air openings between said apertured duct means with saidopenings being disposed toward the outer portions of the spaces betweensaid apertured duct means with the remaining portions of said spacesbeing closed such that the relationship of said spaced apertured ductmeans, said return openings and a web located adjacent to the dryersurface form an independent closed air circulation system for drying theweb.

2. Apparatus as claimed in claim 1 further including an adjustablebaffle lying adjacent and outwardly of the dryer surface, the saidbaffle being movable to close a part of the dryer surface as required.

3. Apparatus as claimed in claim 1 wherein said air supply duct means isdefined, in part, by walls of said cabinet, and the spaced aperturedduct means defining a portion of a wall of said cabinet.

4. Apparatus as claimed in claim 3 further comprising a return air ductmeans operably connected with said return air openings, and said returnair duct means and said air supply duct means being disposed whollywithin said cabinet.

5. Apparatus as claimed in claim 1, wherein said air supply duct meansincludes two outlet ports communicating with said apertured duct means,an inclined baffle means in air supply duct means and positionedadjacent the first of said outlet ports relative to thedirection ofairflow, said baffle means being adapted to deflect air through saidfirst of said outlet ports, and said air supply duct means being ofreduced transverse cross section beyond said baffle means.

6. Apparatus as claimed in claim 1 wherein an additional apparatus isdisposed above and in spaced disposition to said first-mentionedapparatus to define a web receiving opening therebetween, the said twoapparatuses being joined along corresponding lateral edges thereof.

7. The combination as claimed in claim 6 including an adjustable bafflearrangement adapted to close the web receiving opening laterallyoutwardly of a web passing therebetween.

8. Apparatus as recited in claim 7 including a webprogressing meansextending through said web receiving opening and said web-progressingmeans being adjustable laterally so as to adapt for webs of differingwidths.

9. The combination as claimed in claim 7 including a further adjustablebaffle arrangement extending between the dryer apparatuses and lying inthe direction of movement of the web, the said further arrangement beingadapted to separate the air circulation in the apparatuses and to limitheat losses at the edges of the web.

10. The combination as claimed in claim 9 wherein the further adjustablebaffle arrangement includes a first part extending between theindividual apparatuses and a second part lying between such apparatusesand in a plane substantially parallel to the dryer surfaces, the secondsuch part comprising a plurality of elongate elements pivotallyconnected in edgeto-edge configuration.

11. Apparatus as claimed in claim 1 including heat exchange means in thepath of the air, such means being adapted to apply heat to or to removeheat from such air during the circulation thereof.

12. Apparatus for drying sheet material as claimed in claim 1 incombination with at least one additional such apparatus arranged inside-by-side disposition relative thereto.

13. The combination as claimed in claim 12 wherein each successiveapparatus is reversed relative to the previous apparatus.

14. The combination as claimed in claim 12 wherein air exchange meansare provided between each succeeding apparatus and the previousapparatus, such means being adapted to transfer air between theapparatuses.

1. Apparatus for drying sheet material comprising a cabinet havingoppositely disposed end walls and sidewalls, air supply duct meanswithin said cabinet for supplying a source of high pressure drying air,a dryer surface including a plurality of spaced apertured high pressureduct means operatively connected with said air supply duct means andhaving their apertures disposed for directing drying air toward thesurface of a moving web, said apertured duct means being disposed at aninclined angle to a line extending between and at right angles to saidsidewalls of said cabinet such that successive areas of said aperturedduct means overlap said web relative to the direction of travel Of saidweb, return air openings between said apertured duct means with saidopenings being disposed toward the outer portions of the spaces betweensaid apertured duct means with the remaining portions of said spacesbeing closed such that the relationship of said spaced apertured ductmeans, said return openings and a web located adjacent to the dryersurface form an independent closed air circulation system for drying theweb.
 2. Apparatus as claimed in claim 1 further including an adjustablebaffle lying adjacent and outwardly of the dryer surface, the saidbaffle being movable to close a part of the dryer surface as required.3. Apparatus as claimed in claim 1 wherein said air supply duct means isdefined, in part, by walls of said cabinet, and the spaced aperturedduct means defining a portion of a wall of said cabinet.
 4. Apparatus asclaimed in claim 3 further comprising a return air duct means operablyconnected with said return air openings, and said return air duct meansand said air supply duct means being disposed wholly within saidcabinet.
 5. Apparatus as claimed in claim 1, wherein said air supplyduct means includes two outlet ports communicating with said aperturedduct means, an inclined baffle means in air supply duct means andpositioned adjacent the first of said outlet ports relative to thedirection of airflow, said baffle means being adapted to deflect airthrough said first of said outlet ports, and said air supply duct meansbeing of reduced transverse cross section beyond said baffle means. 6.Apparatus as claimed in claim 1 wherein an additional apparatus isdisposed above and in spaced disposition to said first-mentionedapparatus to define a web receiving opening therebetween, the said twoapparatuses being joined along corresponding lateral edges thereof. 7.The combination as claimed in claim 6 including an adjustable bafflearrangement adapted to close the web receiving opening laterallyoutwardly of a web passing therebetween.
 8. Apparatus as recited inclaim 7 including a web-progressing means extending through said webreceiving opening and said web-progressing means being adjustablelaterally so as to adapt for webs of differing widths.
 9. Thecombination as claimed in claim 7 including a further adjustable bafflearrangement extending between the dryer apparatuses and lying in thedirection of movement of the web, the said further arrangement beingadapted to separate the air circulation in the apparatuses and to limitheat losses at the edges of the web.
 10. The combination as claimed inclaim 9 wherein the further adjustable baffle arrangement includes afirst part extending between the individual apparatuses and a secondpart lying between such apparatuses and in a plane substantiallyparallel to the dryer surfaces, the second such part comprising aplurality of elongate elements pivotally connected in edge-to-edgeconfiguration.
 11. Apparatus as claimed in claim 1 including heatexchange means in the path of the air, such means being adapted to applyheat to or to remove heat from such air during the circulation thereof.12. Apparatus for drying sheet material as claimed in claim 1 incombination with at least one additional such apparatus arranged inside-by-side disposition relative thereto.
 13. The combination asclaimed in claim 12 wherein each successive apparatus is reversedrelative to the previous apparatus.
 14. The combination as claimed inclaim 12 wherein air exchange means are provided between each succeedingapparatus and the previous apparatus, such means being adapted totransfer air between the apparatuses.